1. Field of the Invention
The subject invention relates generally to a segmented air distribution bar and, more particularly, to a segmented air distribution bar having air control valves along the length of the bar to enable a user to incrementally adjust the amount of air that is distributed across the width of a roller in a printing press.
2. Background of the Related Art
During offset printing it is not uncommon to develop a build-up of excess dampening solution in the ink on the rollers of the printing press. Its occurrence is inherent to the printing process. Such a build-up, however, does not occur evenly across the width of the rollers. When an excessive amount of dampening solution is picked up by ink, it becomes water logged and breaks down. This is commonly called over-emulsification. The results are extreme ghosting and loss of color density in the print, mottled print, ink piling on the inked rollers, and sheet curl resulting in misregistration and paper feed problems. To eliminate the problems, press operators will usually have to clean the entire ink train and dampener and then replenish the ink and dampening solution fountains. This work stoppage results in product delivery delays and measurable economic loss.
Attempts have been made to prevent excess dampening solution buildup and/or remove the excess dampening solution from over emulsified ink. One method is to install an air bar that directs a stream of air against the surface of one or more inked rollers to force evaporation of excess solution. Two inventions that exemplify this method are disclosed in U.S. Pat. No. 4,524,689 to Lemaster and U.S. Pat. No. 5,085,142 to Smith. Other attempts have been made to prevent excess dampening solution buildup and/or remove the excess dampening solution from over emulsified ink as exemplified in U.S. Pat. No. 5,454,310 to Hayes.
The present invention incorporates a so-called “air-knife” or “air amplifier” of the sort which drives a relatively small volume of air along a wall surface, such that the air adheres to that wall surface. This phenomenon is called the “coanda” effect. This small volume of air creates suction in the adjacent air which pulls in very high volumes of air along with the relatively small volume of air. Amplifications of air volumes on the order of 30 to 1 may be achieved with such air amplifiers.
The structure necessary to achieve the coanda effect includes essentially a thin, elongated slot or nozzle formed in a housing member adjacent to a wall face that curves around a bend. Typically, this bend can be up to 90 degrees. A relatively high-velocity, relatively low-volume air flow is driven along that curved wall face from the slot. By maintaining the slot to a desired relatively thin opening, and by controlling the contour of the wall face, it is possible to ensure that the relatively high-velocity, relatively low-volume air adheres to the wall face and is driven around the curve of the wall face. This, in turn, creates a suction adjacent to the slot which entrains a relatively high quantity of air.
The structure of the amplifier itself is known to those of ordinary skill in the art, and is commonly available on the market. One such amplifier is available under the trade name Exair Air Knife from Exair Corporation (Cincinnati, Ohio). Those of ordinary skill in the art will be aware of the dimensions and parameters of operation necessary to create the coanda effect and resulting air amplification results.
A device that makes use of the coanda effect is disclosed in U.S. Pat. No. 5,313,685, to Sundwiger Eisenhutte, the contents of which are incorporated by reference herein. The device is for removing liquid from the surface of a moving steel strip by means of air blown onto the moving strip from a device having a slot nozzle which is disposed transversely to the direction in which the strip is moving and is directed at the surface of the strip at an angle of between about 45 and 90 degrees opposite to the direction of the strip movement. The device further includes a means for suctioning off any liquid that is removed from the surface of the strip.
Another device that makes use of the coanda effect is disclosed in U.S. Pat. No. 5,490,300, to Paul Horn, the contents of which are incorporated by reference herein. The device is disposed adjacent to a web of material that is to be cleaned. A relatively small volume of compressed air is driven from a slot onto a curved wall surface. The coanda effect causes that compressed air to adhere to the wall, and causes a suction creating a relatively high-volume air flow upstream from the slot to be drawn along with the small volume of air adhering to the wall. The high-volume amplified flow of air is drawn along the surface of a web of material to be cleaned to entrain impurities from the web of material to be cleaned. A vacuum source is mounted adjacent to the end of the wall such that impurities are drawn into the vacuum source and removed from the area. In addition, ionized particles are directed into the relatively high-volume air flow to increase the cleaning efficiency of the system.
Another device that makes use of the coanda effect is disclosed in U.S. Pat. No. 5,491,602, to Paul Horn, et al., the contents of which are incorporated by reference herein. More particularly, disclosed is an air amplifier system incorporating an ionizing device including a converter driven by the compressed air being directed to an air distributor. The converter provides the power source for the ionizing apparatus. In this way, the air distributor and ionizing apparatus can be an easily contained unit. The system may comprise a turbine which is electrically connected to an ionizing apparatus, such as an ionizing bar.